U.S. patent application number 13/204576 was filed with the patent office on 2012-02-09 for spare part for disc refiners for the production of paper.
This patent application is currently assigned to OFFICINE AIRAGHI S.R.L. Invention is credited to Luca Ghibellini, Michele Ghibellini.
Application Number | 20120032010 13/204576 |
Document ID | / |
Family ID | 43589915 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120032010 |
Kind Code |
A1 |
Ghibellini; Michele ; et
al. |
February 9, 2012 |
SPARE PART FOR DISC REFINERS FOR THE PRODUCTION OF PAPER
Abstract
A spare part for disc refiners, in particular a stator and/or
rotor used in a disc refiner for the preparation of paper pulp,
where the stator and/or rotor each comprise a disc-shaped metallic
element with a refining blade surface having alternating blades and
grooves, where the rotor is designed to be driven and rotated
around its own axis of rotation which passes through the centre of
the disc-shaped element so that the rotor blades perform a rotary
movement in front of the stator blades with a suitable air gap in
between. The spare part is characterised in that the blade surfaces
have a pre-set angle greater than 0.degree. with respect to a plane
perpendicular to the rotor axis of rotation, which enables the
achievement of major advantages in terms of the quantity and
quality of the refined product, and the potential to reduce the
energy consumed.
Inventors: |
Ghibellini; Michele; (San
Giovanni Lupatoto (VR), IT) ; Ghibellini; Luca; (San
Giovanni Lupatoto, IT) |
Assignee: |
OFFICINE AIRAGHI S.R.L
San Giovanni Lupatoto
IT
|
Family ID: |
43589915 |
Appl. No.: |
13/204576 |
Filed: |
August 5, 2011 |
Current U.S.
Class: |
241/244 |
Current CPC
Class: |
D21D 1/306 20130101 |
Class at
Publication: |
241/244 |
International
Class: |
D21D 1/30 20060101
D21D001/30 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 6, 2010 |
IT |
VR 2010 A 000165 |
Claims
1. A spare part for disc refiners, in particular a stator and/or
rotor used in a disc refiner for the preparation of paper pulp,
where the stator and/or rotor each comprise a disc-shaped metallic
element with a refining blade surface having alternating blades and
grooves, where the rotor is designed to be driven and rotated
around its own axis of rotation which passes through the centre of
the disc-shaped element so that the rotor blades perform a rotary
movement in front of the stator blades with a suitable air gap in
between, the spare part being characterised in that the blade
surfaces have a pre-set angle greater than 0.degree. with respect
to a plane perpendicular to the rotor axis of rotation.
2. The spare part according to claim 1, characterised in that the
blade surfaces seen in a side cross section have a rectilinear
and/or curvilinear profile.
3. The spare part according to claim 2, characterised in that the
side cross section profile is uniformly rectilinear and has a
constant angle.
4. The spare part according to claim 2, characterised in that the
side cross section profile comprises a curved line.
5. The spare part according to claim 2, characterised in that the
side cross section profile comprises rectilinear segments angled
differently.
6. The spare part according to claim 2, characterised in that the
side cross section profile comprises an assembly of rectilinear and
curved elements.
7. The spare part according to claim 2, characterised in that the
side cross section profile substantially has a saw-tooth shape.
8. The spare part according any one of the foregoing claims,
characterised in that it is designed to be mounted inside a disc
refiner for the preparation of paper in the same space as that
occupied by the traditional disc that the spare part substitutes
and without requiring any further modification to the refiner.
Description
[0001] The present invention refers to a spare part for disc
refiners used in the production of paper.
[0002] In particular, the present invention refers to a spare part,
consisting of, respectively, a stator and/or a rotor used in a disc
refiner for the preparation of paper pulp. The pulp enters them
from one end and exits from other side, passing through a rotating
body equipped with blades or an alternation of solids and voids
(blades, holes, etc. derived from mechanical processing and made on
one face or both) and a shell which has fixed counter-acting
blades. Such solid and void alternations are conventionally defined
as "blade patterns".
[0003] The present invention has applications in applied mechanics
in the field of paper making.
BACKGROUND ART
[0004] The refining process represents the only phase of the entire
paper making process in which the fibres are physically modified.
It consists of a mechanical action in which the fibres are
processed through two or more pieces of consumable blades (rotor or
stator).
[0005] The pulp must pass through the existing spaces between two
opposing spare parts.
[0006] In this passage between the blades of the rotor and the
stator, the fibres are subject to high levels of compression,
friction and cutting, which determine major (and unique)
modifications to their physical structure.
[0007] The refinement causes modifications to the fibres of a
physical nature which can appear more or less intense in measure
depending on the conditions adopted for the treatment. Such
modifications may be briefly summarized as: [0008] a) Swelling and
hydration; [0009] b) Increases in plasticity and flexibility;
[0010] c) External fibrillation; [0011] d) Internal fibrillation;
[0012] e) Cutting and shortening of the fibres; [0013] f) Formation
of fine particles.
[0014] Modern low-density refiners may be classified in 2 principle
classes: conical and disc. In general, each piece of machinery,
whether conical or disc, is constructed of two consumable pieces: a
fixed part called a "stator" and a rotating part which is defined
by the term "rotor".
[0015] Both of them have on one side a "blade pattern", alternately
consisting of bars and grooves.
[0016] The width, the length and the inclination of the bars (or
blades) and the width and depth of the empty spaces (or duct
grooves) constitute the configuration of the spare parts upon which
the performance of the refiner depends.
[0017] On conical refiners the principal characteristic is the
angle of the cone.
[0018] The first conical refiners had a narrow angle: they are in
fact assembled with a cone which forms an approximately 10.degree.
angle with respect to the axis of rotation, with spare parts which
are quite rough and for this reason they are considered strong
action cutting refiners.
[0019] Despite this, if used with spare parts with narrow bars,
they give optimal results with all types of fibres.
[0020] The difficulty of the substitution of spare parts has
resulted in the substitution of these refiners with those which are
more functional having a medium angle, described below.
[0021] Another type of conical refiner is the so called large angle
refiner, the structure of which is similar to that with a narrow
angle but is assembled with spare parts with an approximate
30.degree. angle with respect to the axis of rotation.
[0022] The most recent versions and those which are more widely
used for low density pulps are medium angle refiners which are
characterized by cones which form an approximate 20.degree. angle
with the axis of rotation and, above all, mechanics which permit
easy access to the zone of the spare parts therefore reducing
maintenance times.
[0023] The principal parts which constitute a conical refiner are:
[0024] 1. a shell with a pulp entry and exit; [0025] 2. a conical
rotor; [0026] 3. a conical stator; [0027] 4. a regulation mechanism
of the rotor.
[0028] The conical spare parts are used to limit axial forces.
[0029] In fact, the effective forces in play during this type of
refinement divide into one which is axial (parallel) and one which
is perpendicular to the refining surface.
[0030] In terms of disc refiners, the principle of the latter is
similar to that which governs the conical refiners.
[0031] The pulp which is to be refined in this case is fed
centrally to the area between the discs and, due to the centrifugal
force produced by the rotation of the rotor disc, the pulp tends to
move toward the periphery, due to the rubbing action between the
blade patterns of the stator discs (fixed) and the rotor discs
(mobile).
[0032] Given their high peripheral speed these machines usually
guarantee optimal production.
[0033] Taking into account the spare part discs, this type of
refiner is distinguished for its very compact construction.
[0034] However, the loss of "no load" pumping power is higher in
comparison with other machines.
[0035] Normally, it seeks to limit this loss by using shallow
grooves.
[0036] Disc refiners have three basic layouts depending on the type
of spare part used: [0037] refiners with a fixed disc and a
rotating disc; [0038] refiners with two rotating discs and two
fixed discs; [0039] multi-disc refiners (with more than two
rotor-stator pairs).
[0040] Disc refiners can be further subdivided depending on the
direction of the flow of pulp inside the refiners themselves.
[0041] In terms of the quality of the refinement, it is recognized
that there is a substantial difference between refining with
discoid spare parts and refining with conical ones.
[0042] In fact, due to the type of flow found between the rotor and
the stator, and also due to the vortices and the centrifugal forces
that they generate, not all of the fibres treated in the disc
refiner can be refined; some can, in fact, follow the cavities of
the plate from the entry to the exit.
[0043] In fact, it has been demonstrated that, in some cases, a
considerable number of fibres are not refined in the first passage
through the disc refiner.
[0044] As a consequence, the refining efficiency and the energy
efficiency are relatively low.
[0045] In a disc refiner, therefore, it is probable that the fibres
which come into contact with the blades tend to be over-refined to
compensate for those which have not been refined in a way which
achieves the desired pulp freeness (.degree. SR).
[0046] This causes an excessive formation of fines, a weakening of
the refined fibres and energy inefficiency applied to the
fibre.
[0047] This all happens on a much smaller scale in the conical
spare part, because the hydrodynamic forces in play tend to push
the fibres from the rotor spare part towards the stator spare part,
creating a sort of thrust and successive slippage of the pulp which
avoids the immediate outflow from the spare parts of the latter,
therefore retaining the majority of the pulp.
[0048] In fact, the centrifugal force and the flows of the vortices
on the inside of the conical refiner create and facilitate the
passage of the fibres from the grooves toward the bars.
[0049] This creates, therefore, a type of spiral movement around
the part, as opposed to what happens with the discs, given that the
pulp is rapidly pumped towards the exterior.
[0050] The conical refiner, therefore, permits an improvement in
processing, a more complete and uniform treatment of the fibres and
an improvement in energy efficiency which is also due to the fact
that the fibres are in contact with the blade for a longer
time.
[0051] In the refinement process itself the fibres are not refined
individually but in flakes.
[0052] In the range of fibrous pulp with a consistency between 2%
and 6%, where the low density refinement is located, the fibres are
not free to move independently.
[0053] Inside the fibrous suspension, a non-homogenous structure
composed of fibres is created which, being close to one another,
interact between themselves and create flakes; such flakes form and
break up continually under the effect of the different intensities
of the cutting forces which exist in the grooves and in the
refining zone.
[0054] The size and the thickness of the flakes (1-5 mm) are much
larger than those at the distance which is between the blades of
the stator and the rotor in the refinement phase (usually even less
than a few tenths of a millimetre.)
[0055] For this reason, the probability that the flakes in this
form can be driven between the edges of the blades of the rotor and
the stator is not very high. To promote the effects of the
refinement (external fibrillation, delamination of the internal
structure of the wall, cutting of the fibres, etc.) the operative
energy is transferred from the refiner to the pulp in the following
three modes:
[0056] in the moment in which the flake is caught between the edges
of the two bars, of the stator and the rotor, and the fibres are
subject to cutting actions;
[0057] when the bars are overlapped and part of the flake is found
between the edge of the tooth of the rotor and the surface of the
stator and then between the two surfaces; in this phase the elastic
flakes of the fibre are compressed between the blades with a
dynamic filtration of the water from the fibres;
[0058] with the continuous fibre-fibre friction action, inside the
flakes, in the flow of the pulp which passes through the
cavities.
[0059] During the design stage of the rotors and stators of the
refiners, the dimensions of the bars and grooves (i.e. the blade
pattern) and the angle of the blade pattern itself determine the
"cutting edge length" [L].
[0060] This length is measured in metres or kilometres.
[0061] The cutting edge length L represents, therefore, the total
length of the "contact" between the rotor and stator blades at each
turn of the rotor and is expressed as follows:
(DR.times.nB.sup.2).times.ni/cos .alpha. [L]
where: [0062] DR=radial increment of the teeth (m); [0063]
nB=number of blades for each radial increment (number of
teeth/sector.times.number of sectors); [0064] ni=number of
interfaces (for 4 discs, ni=2); [0065] .alpha.=average angle
between teeth and the radius of the tip of the same tooth.
[0066] Refining processes involve the use of considerable amounts
of energy. In effect, refining accounts for 25-30% of the total
requirement of electric energy in paper making and is therefore an
important factor.
[0067] The energy consumed during the refining process is therefore
a major factor influencing the results of the refining.
[0068] With the machines in use today, it is not possible to
transmit all of the energy which is produced to the refinement of
the pulp, and a part of the energy is dissipated in the form of
friction and heating of the fibrous suspension.
[0069] In order to determine the efficiency of the refining process
with sufficient precision, it is important to know the real load
power of the refiner used.
[0070] The power required to rotate freely, which is subtracted
from the current consumption in the refining phase, is the sum of
the electric losses of the motor, of the mechanical losses, due to
friction in the motor and in the refiner, and of the hydraulic and
circulating power, which is the quantity of energy absorbed by the
hydraulic action due to the effect of turbulence or pumping.
[0071] The no-load power depends mainly on the diameter and rotary
speed of the rotor part, but it can also be significantly affected
by the configuration of the bars and grooves (i.e. by the blade
pattern).
[0072] Factors like flow, consistency of the pulp and air gap
(meaning the distance between the stator disc and rotor disc) have
a relatively minor importance.
[0073] The effective power applied, therefore, which determines the
changes of the properties of the pulp, is constituted by the power
consumption in the refining phase from which the no-load power must
be subtracted.
[0074] For these reasons it is important to know the no-load power
consumed by a refiner with its spare parts, and, moreover, it is
important to take into account the effective wear of the spare
parts.
[0075] No-load power can be determined through empirical
measurements or calculated using theoretical formulas.
[0076] The factor to be noted, however, is that for each piece of
machinery with a spare part, the no-load (NL) power can vary
considerably over time, which means that it has a high value when
the spare parts are new and a lower value when they are worn
down.
[0077] Given that it is quite complex to obtain accurate
measurements, it is often easier to trust in calculations of values
through universally recognized formulas, such as the following:
NL=KD.sup.4N.sup.2,57 [0078] the no-load power NL is expressed in
kW; [0079] K is a constant which varies between conical and disc
refiners; [0080] D is the diameter of the part expressed in meters;
[0081] N is the number of repetitions per second.
[0082] This formula shows how the diameter of the disc is a
decisive variable in the determination of the no-load power
consumption.
[0083] In practice, however, the experimental formula generally
used for the determination of the dissipated no-load power is the
following:
NL=(3.083.times.10.sup.-13)D.sup.4.249N.sup.3
where: [0084] NL is expressed in HP; [0085] the constant K is
indicated as 3.083.times.10.sup.-13; [0086] D is the diameter of
the part expressed in inches; [0087] N is the number of repetitions
per minute.
DESCRIPTION OF THE INVENTION
[0088] The present invention provides new spare parts for disc
refiners composed of at least one rotor and at least one stator
which, thanks to the special configuration of the blade surface,
and without any modification to the existing structure of the
machinery, simultaneously permits the following:
[0089] improved refining;
[0090] substantial energy savings.
[0091] This is achieved through a spare part (stator/rotor) for
disc refiners having the characteristics described in the main
claim.
[0092] The dependent claims outline particularly advantageous
embodiments of the spare parts described above.
[0093] According to a particularly advantageous embodiment of the
invention, and in strong contrast with the configurations present
in the spare parts for disc refiners of the known type--in which
the respective blade surfaces of the rotor and of the stator are
situated on planes perpendicular to the axis of rotation of the
rotor--the spare parts for disc refiners according to the present
invention have blade surfaces which have a preset angle with
respect to the planes which are perpendicular to the axis of
rotation of the rotor.
[0094] In a further particularly advantageous embodiment of the
invention, and also in stark contrast with the current
configurations of the spare parts for disc of the known type, the
spare parts for disc refiners according to the present invention
have blade surfaces with a generally curvilinear or irregular
profile.
[0095] The embodiments described above allow one to obtain,
alternatively or synergistically: [0096] a considerable increase in
the cutting edge length L, that increases the efficiency of the
refining action of the disc refiner and, at the same time, allows
one to increase the production of a given refiner as though it were
equipped with discs with larger diameters--yet without requiring
the substitution of the entire refiner with one of a larger size;
or [0097] the possibility to use, at the same cutting edge length,
discs with smaller diameters for the same refiner, which implies
considerable energy savings; or [0098] to improve the refining
action of any disc refiner given that the configuration according
to the invention makes it more difficult for the pulp to exit and,
holding it inside the spare parts for a longer time, the latter is
treated in an improved and more uniform way.
[0099] In any case, as previously mentioned, it is necessary to
emphasise how the spare parts are configured to be inserted into
existing disc refiners according to the present invention, without
requiring any further conversion or special maintenance of the
refiner other than the substitution of the worn discs. This is
because the pair of spare parts according to the present invention
have the same thickness as the pairs they are designed to
substitute.
DESCRIPTION OF THE DRAWINGS
[0100] Further features and advantages of the invention will become
apparent from the following description of some embodiments of the
invention with reference to the annexed drawings, given purely by
way of a non-limiting example, in which:
[0101] FIG. 1 shows a Cartesian diagram which shows the advantages
of using a refining disc equipped with inclined blade pattern
surfaces according to the present invention;
[0102] FIGS. 2a, 2b, 2c, 2d and 2e show side view cross sections of
five embodiments of the spare parts, in particular the refining
discs, having inclined, rectilinear profiles (FIG. 2e) and curves
or mixtilinear profiles (FIG. 2a, 2b, 2c, 2d) according to the
present invention;
[0103] FIG. 2f shows a side cross section of a known refining disc,
therefore at a perpendicular profile to the axis of the disc
itself; and
[0104] FIGS. 3a and 3b are perspective drawings showing a disc in
the form of a rotor and one in the form of a stator according to
the present invention, with inclined rectilinear profiles, which
are usable as spare parts for a disc refiner for the refining of
paper.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0105] In FIG. 1, a Cartesian diagram with nonessential errors
shows how, at an equivalent cutting edge length, it would be
possible to obtain a smaller disc diameter acting on the angle of
inclination (x) of the blade pattern with respect to a blade
pattern which is flat and perpendicular to the axis of the disc
itself.
[0106] Using the known mathematical formula,
cos ( x ) = OC _ OD _ ##EQU00001##
and keeping as a constant the cutting edge length, it is possible
to derive the angle x of inclination of the blade pattern
corresponding to a given cutting edge length, which corresponds to
a predetermined diameter.
[0107] By decreasing the diameter of the disc, at the same cutting
edge length, it is possible to determine a consistent conservation
in terms of dissipated electric energy in no-load conditions.
Clearly, a greater inclination of the blade pattern corresponds to
a smaller disc diameter, but one must take into account a
constraint in terms of the machine stroke, which obviously cannot
exceed the dimensions provided in the refiner.
[0108] It should be noted that by using the same formula, and by
keeping the diameter of the disc constant in this case, it is also
possible to understand how it would be possible to obtain greater
cutting edge lengths, with respect to traditional disc types, with
a spare part with an inclined blade pattern according to this
invention.
[0109] This opens up very interesting opportunities from both a
manufacturing and commercial point of view. In fact, with the same
disc diameters, a given refiner equipped with spare parts according
to the present invention could provide better performance in terms
of both the quantity of and the quality of refined products,
thereby obviating the need to substitute the refiner with one of a
larger size when it is necessary to increase production.
[0110] The FIGS. 2a to 2e show some examples of practical
embodiments of the spare parts for disc refiners which are
obtainable according to the present invention.
[0111] It is worth comparing these figures with FIG. 2f, which
shows in a traditional disc type, with a 26-inch diameter for
example. In particular:
[0112] the disc shown in FIG. 2a has, for example, a 24'' diameter
and a rectilinear blade pattern with a uniform inclination angle
(as do the discs shown in FIGS. 3a and 3b);
[0113] the disc shown in FIG. 2d has, for example, a 22'' diameter
and a uniformly curved blade pattern profile;
[0114] the disc shown in FIG. 2c has, for example, a 22'' diameter
and a blade pattern profile composed of differentially inclined
rectilinear segments;
[0115] the disc shown in FIG. 2b has, for example, a 20'' diameter
and a blade pattern profile comprising both curved and rectilinear
elements; and
[0116] the disc shown in FIG. 2a has, for example, a 20-inch
diameter and a substantially saw-toothed blade pattern profile.
[0117] Clearly, the profile shapes and the diameters of the discs
indicated above are example embodiments of the invention which can
be applied to any typology of refining discs; the diameter and
shape of the discs can be freely adapted to particular design needs
to take into account the quantity and quality of the product to be
refined.
[0118] The spare parts according to the present invention can be
manufactured using various methods and technologies in accordance
with design requirements.
[0119] The invention as described above refers to its preferred
embodiments.
[0120] Naturally, while the principle of the invention remains the
same, the details of construction and the embodiments may widely
vary with respect to what has been described and illustrated purely
by way of the example, without departing from the scope of the
present invention.
* * * * *